I. Field of the Invention
This invention relates generally to high pressure industrial pumps, and more particularly to an improved means for introducing one or more chemicals in metered amounts into the fluid stream being delivered through the pump's high pressure outlet port.
II. Discussion of the Prior Art
In certain system applications, it is desired that a first fluid, e.g., water, be delivered at a high pressure and that a chemical, e.g., liquid soap, be mixed with the high pressure fluid stream. Such an arrangement is commonly used in high pressure washing equipment. For example, in automatic car wash systems, it is desirable to deliver a soap solution from a dispensing nozzle at a pressure in the range of from 800 to 1,000 psi. In prior art arrangements, a venturi-type injector is commonly used to draw liquid soap concentrate from a supply tank and to mix it with the water stream as it passes through the throat of the venturi. For a venturi injector to work, however, it is requirement that there be a significant pressure drop across it to create the necessary vacuum for drawing the soap concentrate from its supply tank. This, of course, detracts from the pressure available to dislodge the dirt and grime from the object being washed.
In still another prior art arrangement, the chemical source is placed at a higher elevation than the pressure pump and a needle valve in a supply line is used to control the flow of soap concentrate into the wash stream at the inlet of the pump.
It was also known prior to my invention that the suction stroke of a positive displacement pump can be used to create the requisite negative pressure for drawing the soap concentrate into the cylinder, again through a needle valve assembly used in place of the usual inlet poppet valve which opens on the suction stroke but closes on the pressure stroke. Such a needle valve assembly is relatively costly and may be easily damaged by improper or frequent opening and closing thereof.